1. Field of the Invention
This invention relates to a process for drying a coated web such as a photographic photosensitive material.
2. Description of Prior Art
Various photographic photosensitive materials and other materials are manufactured by drying a continuous web such as a plastic support or a paper support on which one or more coating compositions are applied. This composition is generally produced by dissolving or dispersing prescribed components in an organic solvent. The coated web is dried by blowing hot air or by irradiation with infrared light. In such drying methods, when the concentration of the organic solvent vapor becomes high, an explosion occurs. Therefore, a large quantity of air was introduced into the oven, and thereby the concentration of the organic solvent vapor was controlled so as to be kept lower than one third of the explosion limit. As a result, a lot of thermal energy was consumed for heating of the air for dilution and for incineration of a large amount of the exhaust gas, in addition to the energy required for the evaporation of the solvent. Various investigations for solving this problem have been made, and for example, recovery of heat of the exhaust gas by using a heat exchanger and a method of using water as the solvent have been proposed.
On the other hand, it is known that, in the drying process of a continuous coating on a metallic strip, an explosion of a solvent is prevented by blowing a hot inert gas into an oven and thereby the air for dilution is not added (U.S. Pat. No. 3,909,953). In this method, the exhaust gas is mixed with air, and the organic solvent in the gas is incinerated to produce an inert gas. The heat of the inert gas is utilized for the drying of the metallic strip by returning the incinerated gas into the oven, and excess heat is recovered by a heat exchanger and utilized.
In the recovery of heat of the exhaust as by using a heat exchanger, the yield of heat recovery is usually only about 50 to 60%. The cost of equipment is expensive, because a big heat exchanger is necessary. In the method of using water as the solvent, consumption of thermal energy is increased by evaporating the water. In the foregoing method to incinerate the exhaust gas, the cost of equipment is expensive, because a big incinerator and heat exchanger are necessary. It is also a problem that the whole amount of the valuable organic solvent is incinerated.